Portland, Ore. • Oregon's attorney general will not defend the state's ban on gay marriage, arguing it cannot withstand a federal constitutional challenge.

Ellen Rosenblum joins fellow Democrat attorneys general in at least five other states who have pledged not to defend state bans on gay marriage.

"State Defendants will not defend the Oregon ban on same-sex marriage in this litigation," Rosenblum said in the documents filed in federal court on Thursday. "Rather, they will take the position ... that the ban cannot withstand a federal constitutional challenge under any standard of review."

Rosenblum's decision comes less than one month after a federal judge decided to consolidate two lawsuits alleging Oregon's ban violates the U.S. Constitution.

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Portland attorneys filed the first lawsuit in October, on behalf of two women who have been in a relationship for more than 30 years and another couple who sought to have their union recognized in Oregon. The American Civil Liberties Union then filed a lawsuit two months later on behalf of two same-sex couples.

The first suit argued that limiting marriage to opposite-sex couples violates the due process and equal protection rights of same-sex couples. "Oregon law treats similarly situated people differently without legal justification by providing civil marriage to heterosexual couples but not to gay and lesbian couples," the suit alleged.

Last year, Rosenblum signed on to U.S. Supreme Court briefs arguing it was unconstitutional to deny gays the right to marry.

Nationally, attorneys general in five states — Virginia, Pennsylvania, California, Illinois and Nevada — have declined to defend same-sex marriage bans against lawsuits filed by gay couples, while a sixth, in New Mexico, challenged longstanding legal interpretations that said such unions were impermissible there.

The Democrat running for Colorado attorney general called on the current Republican officeholder to stop defending the state's prohibition. And in Texas, Democratic gubernatorial candidate Wendy Davis demanded that her likely Republican opponent, Attorney General Greg Abbott, do the same.

Conservatives have accused them of shirking their sworn responsibility. They say attorneys general, as the top lawyers for their states, are supposed to represent their client — the state — regardless of personal beliefs.

But the attorneys general say the legal case against gay marriage is crumbling and that it would be improper for them to argue positions they have concluded are clearly unconstitutional.